Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $31.35   13.758%   $35.6631   $35.66   $35.65   $35.70  
  Purchase #2 $233.37   11.874%   $261.0804   $261.08   $261.10   $261.10  
  Purchase #3 $125.49   3.392%   $129.7466   $129.75   $129.75   $129.70  
  Purchase #4 $67.67   9.413%   $74.0398   $74.04   $74.05   $74.00  
  Purchase #5 $229.90   9.295%   $251.2692   $251.27   $251.25   $251.30  
  Purchase #6 $246.27   11.285%   $274.0616   $274.06   $274.05   $274.10  
  Purchase #7 $215.73   11.309%   $240.1269   $240.13   $240.15   $240.10  
  7 purchase totals = $1,149.78       $1,265.9876   $1,265.99   $1,266.00   $1,266.00